As part of a preamplifier project for my home audio system I am seeking a single bipolar op amp to use in a non-inverting configuration. I hope to find one that is not too difficult to use, especially since I plan to build the preamp point-to-point (no pcb).
This is my list of requirements:
Single amplifier
Bipolar input
8-pin inline package (not surface mount)
Output voltage in the 12V range for 15V supply
Output current in the 35ma range into a 2kohm load
Unity-gain stable
Slew rate not too low (about 15 or above)
Gain bandwidth not too high (about 50 or below)
I have some flexibility in the individual parameters, but these guidelines give a good idea of what I am seeking. To give an example, a single version of National Semiconductor LM4562 (or LME49720/49860) would be ideal. I have performed various searches, but the op amps I have found don't meet my needs in regard to one or more requirements.
Can anyone offer suggestions?
This is my list of requirements:
Single amplifier
Bipolar input
8-pin inline package (not surface mount)
Output voltage in the 12V range for 15V supply
Output current in the 35ma range into a 2kohm load
Unity-gain stable
Slew rate not too low (about 15 or above)
Gain bandwidth not too high (about 50 or below)
I have some flexibility in the individual parameters, but these guidelines give a good idea of what I am seeking. To give an example, a single version of National Semiconductor LM4562 (or LME49720/49860) would be ideal. I have performed various searches, but the op amps I have found don't meet my needs in regard to one or more requirements.
Can anyone offer suggestions?
that LME fails on the output current - many op amps will not manage 35 mA or perform well if used at even 1/2 the data sheet current limit #
some dual op amps (still in 8 pin DIP) with the extra op amp used as a paralleled buffer to double output current may give more choices, requires a couple of small value current summing R between outputs
but common mode input V may limit unity buffer range more than output stage saturation too - another spec to check
http://nwavguy.blogspot.com/2011/08/op-amp-measurements.html is a possibly useful summary
some dual op amps (still in 8 pin DIP) with the extra op amp used as a paralleled buffer to double output current may give more choices, requires a couple of small value current summing R between outputs
but common mode input V may limit unity buffer range more than output stage saturation too - another spec to check
http://nwavguy.blogspot.com/2011/08/op-amp-measurements.html is a possibly useful summary
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Is this a typo, or do I misunderstand the intent? Basic Ohm's Law says this opamp is putting over 2 watts into the 2K ohm load, and would require rail voltages in excess of 70 volts.
Dale
Yes, that's right. Let's wait for majerjack to explain what he meant...
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If the I see an output short circuit current for an opamp, it seems sensible to me to never use more than half that hard limit for "normal" operation.
This would limit most opamps to a maximum operational current of 15mA to 20mA.
Similarly I would set myself an output voltage limit of 2 to 3 volts below the supply rail voltage.
I can usually see this by looking at the plots and seeing where the curves start to become excessive.
Eg,
running a 5534 on +-18Vdc I would expect <15Vpk and <20mA into all loads. BUT NOT AT THE SAME INSTANT.
I would not expect 15Vpk into a 600ohm load.
This would limit most opamps to a maximum operational current of 15mA to 20mA.
Similarly I would set myself an output voltage limit of 2 to 3 volts below the supply rail voltage.
I can usually see this by looking at the plots and seeing where the curves start to become excessive.
Eg,
running a 5534 on +-18Vdc I would expect <15Vpk and <20mA into all loads. BUT NOT AT THE SAME INSTANT.
I would not expect 15Vpk into a 600ohm load.
Apologies for the confusion. I blame it on a hurried posting while preparing to go bring home the bacon.
The op amp will not have to produce 12V nor sink 35mA. Actual numbers will be closer to 6V and 6mA. The previous numbers were shown to give an idea of the output capabilities that I am seeking (quoted from op amp data sheets). I want drive characteristics that will give me headroom to spare.
Thanks to all for the replies and tips.
P.S. Does anyone have experience with the Linear Technology LT1028? It looks promising, but I can't find a maximum output current rating in the data sheet.
The op amp will not have to produce 12V nor sink 35mA. Actual numbers will be closer to 6V and 6mA. The previous numbers were shown to give an idea of the output capabilities that I am seeking (quoted from op amp data sheets). I want drive characteristics that will give me headroom to spare.
Thanks to all for the replies and tips.
P.S. Does anyone have experience with the Linear Technology LT1028? It looks promising, but I can't find a maximum output current rating in the data sheet.
~ 1nV/sqrt(Hz) bipolar op amps are best with low Z source, moving coil phono cartridges, some dynamic microphones and not much else in home audio
already buffered line level audio the noise spec is usually already dominated by the preceding electronics
because the high bias input BJT have high input I_noise that gets converted to V_noise in the source and feedback Z
the LT1028 isn't unity gain stable - but does have a external compensation pin
already buffered line level audio the noise spec is usually already dominated by the preceding electronics
because the high bias input BJT have high input I_noise that gets converted to V_noise in the source and feedback Z
the LT1028 isn't unity gain stable - but does have a external compensation pin
The max output current typically quoted in Data Sheets is seldom very significant to audio amplifier applications. It's a measurement of available current into a short-circuit load, and typically tells you more about the opamp's internal current limiting circuit (and the ability of that circuit to protect the opamp from damage) than it tells about the opamp's ability to drive a load. As the opamp output current approaches the data sheet max - or even a significant fraction of the max, say, half the max - the open-loop gain typically drops, the output distortion rises significantly, and the available output voltage swing is significantly reduced.
If you intend to actually operate the opamp as an audio amplifier, into a load requiring more than a dozen milliamps or so, look for a device specifically rated for that load impedance (or less). Lacking that, look for plots of THD versus load impedance at various output voltage swings.
Dale
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